This invention relates to an improved method and apparatus for providing a random rake finish in the surface of a cast concrete panel.
With the advent of multiple lane, limited access highways for motor vehicles, there has been a growing concern, particularly in urban areas, with respect to the noise generated by traffic on the roadway. Various solutions have been proposed to diminish the noise including the erection of various types and kinds of barriers between the roadway and the area adjacent the roadway. These barriers have been constructed from numerous types of materials including wood, concrete and metallic screen. One of the more popular and useful types of materials used to create such barriers is concrete typically in the form of a cast concrete panel or in the form of layers of concrete and other materials in a panel that is able to withstand weathering yet which provides required sound deadening characteristics, structural integrity and is economical to manufacture, install and service. Originally such cast concrete panels had smooth surfaces. Over time the texture of the surfaces has changed, and the materials used on the surfaces have changed. Thus the esthetic quality of the surfaces has been enhanced by texture, color and otherwise.
One of the popular surface textures associated with precast concrete panels used for traffic barriers is known as the random rake surface finish. That is, a concrete panel is cast in a particular shape and size. Typically, the material being cast includes an aggregate which is maintained in a smooth and fluid cement mixture. After the panel is cast in the desired thickness and shape, and a smooth generally flat uniform surface has been achieved, the surface is textured to a rough or "fuzzy" finish. This finish is produced by use of an asphalt rake, typically a 24" asphalt rake, having every other tine removed therefrom. The rake is manually manipulated by dragging the tines in the surface or outer face of the cast panel. The tines are required to project about 1" below the surface of the panel, and they are moved in a swirling motion in a manner so that the surface will not be gouged and so that tine marks will not be left in the surface. This causes the aggregate in the panel to be randomly distributed and projected from the surface of the panel to provide the desired finish. This finish is thus provided by a random series of projections of the aggregate from the panel surface. After the raking operation is completed the concrete is then allowed to dry normally.
The particular procedure by which such panels are manufactured is exceedingly labor intensive and thus quite costly. Additionally, the variants in finish resulting from the "raking" techniques of individual laborers may become apparent. Thus there may not be a uniform random raking operation performed on the surfaces and the panels will look dissimilar. This is an undesired outcome.
Therefore, there has developed a need to provide a procedure and a mechanism by which a random rake finish can be produced which is uniform, inexpensive, reproducible and not as labor intensive as prior procedures.